1. Field of the Invention
The present invention relates to electromagnetic components. More specifically, the present invention relates to systems and methods for forming conductive patterns in radomes and other electromagnetic components.
2. Description of the Related Art
Electromagnetic (EM) windows, including radomes, IR domes, multi-mode domes, and flat plate EM windows (IR, RF, or multi-mode), hereafter referred to as domes, are structures used to protect electromagnetic devices, such as antennas or sensors mounted on missiles or aircraft, from environmental conditions. The structural and electromagnetic requirements of a dome are usually very stringent. The dome should be made of a material having sufficient strength to withstand weather conditions (rain, wind, hail, etc.) and the imposed aerodynamic loadings. The dome should also exhibit certain electromagnetic properties. For example, domes are typically designed to be transparent to EM signals at the frequencies transmitted and received by the system.
It is highly desirable that the signals can pass through the radome with no reflection or distortion. Since practically all dome materials have a dielectric constant different from that of air, most domes cause some reflections of energy at the dielectric interfaces. In systems where the reflections cannot be tolerated, it has become common practice to embed a wire grid into the dome material itself to aid in the transmission of microwave energy. The embedded wire grid appears inductive to the radio frequency signal and the inductance can be arranged to offset the capacitance of the dome material. By proper design, a dome can be built which will pass a band of frequencies centered on any desired operating radar frequency and/or reject undesirable frequencies.
Traditional radome design uses a dome-like shell of dielectric material having a thickness that is a one-half wavelength of a center frequency of operation for the antenna. The one-half wavelength thickness is optimal for RF (radio frequency) transmittance. For certain applications, it may be desirable to deviate from a traditional radome design for mechanical considerations. For example, it may be desirable to use a much thinner wall than is optimal for RF transmittance. In such cases, a wire grid can be used to compensate and shift the optimal transmittance frequency of the device to the desired operating frequency.
The wire grids should have very precise line widths and spacing for optimal performance. Current methods for fabricating radomes with wire grids, however, are not capable of the high precision and accuracy required. Wire grids are typically placed by hand and glued onto the radome dielectric structures. This method is inherently imprecise as well as expensive. The same is true for IR and multi-mode domes.
A frequency selective surface, comprised of a pattern of conductive elements formed on a dielectric surface, can also be applied on a dome to selectively allow certain signals to pass through while rejecting other signals. Typically, the conductive elements are often configured as closed loops, square loops, or circular loops. Generally speaking, the dimensions and spacing of the conductive elements determine the pass bands and rejection bands.
Frequency selective surfaces are typically fabricated using conventional etching techniques. The accuracy of the frequency selectivity of the surface depends on the precision of the pattern formed on the surface. Any curvature in the surface complicates the pattern and makes the achievement of precise frequency selectivity extremely difficult. This is especially true in the case of complexly curved surfaces typical of dome designs. Currently, there is no known method for patterning curved surfaces to achieve precise frequency selectivity in a cost effective manner.
Hence, a need exists in the art for an improved system or method for forming a conductive pattern for more precisely controlling the electromagnetic properties of a dome.